Federal officials are investigating why a Southwest Airlines flight that was supposed to land at Branson Airport in southwest Missouri instead landed at another airport about 7 miles away that only had about half as much runway. Southwest Airlines Flight 4013, carrying 124 passengers and five crew members, was scheduled to go from Chicago's Midway International Airport to Branson Airport, airline spokesman Brad Hawkins said Sunday in a statement. But the Boeing 737-700 landed at Taney County Airport, which also is known as M. Graham Clark Downtown Airport.